: Aim 1 is to synthesize 18F-labeled androgens for Positron Emission Tomography (PET) imaging of prostate cancer. The steroids include an active androgen as well as prohormones that are metabolically protected to maximize the biological signal. These steroids, labeled at C-7alpha with 18F, will be synthesized and tested for androgen receptor mediated concentration in the prostate of rats and rabbits. Aim 2 is to synthesize 18F and 123I labeled pyridyl and pyrimidyl N-substituted pyrazolo steroids based on the active glucorcorticoid, cortivazol. These steroids, containing N-activated leaving groups in their heterocyclic ring system, are designed specifically for isotope exchange reactions. The steroids are intended as PET or Single Photon Emission Tomography (SPECT) agents for imaging the glucocorticoid receptor rich region of the brain, the hippocampus. Aim 3 is to synthesize and test analogs of E2 that are potent estrogens and yet enzymatically labile which cause them to be converted rapidly into inactive metabolites. They are designed for use as local estrogens.